Conveying devices, such as those which are used for moving objects between different stations in a factory, usually comprise a conveying track in the form of a belt or a chain. The conveying tracks can be recessed in a trench with vertical side surfaces. Alternatively, they can be located on the horizontal upper surfaces of the trench or arranged in some other way. The objects to be conveyed are arranged slidably in relation to the conveying tracks, either directly or via carrying means, which are also known as pallets. A specific type of pallet is a puck, which is a round carrier adapted for smaller and more lightweight objects.
A pallet is conveyed along the conveying device, which comprises different work stations. At a work station, the pallet will be stopped such that the operation may be performed on the transported object. In some cases, the object may pass a specific work station without an operation being performed on the object.
If the conveying device is of a conventional type, in which all work stations are positioned after each other and the operations on the objects are performed synchronous, every pallet will stop at each work station. If no operation is to be performed on an object at a specific work station, the object will have to wait until the operation on the previous object at that work station is ready, until the object can continue. All pallets are in this case released at the same time and moves at the same time. One advantage of such a system is that it is easy to predict the performance of the system. One disadvantage of such a system is that it is not very flexible. If the operation time at a work station is long, all objects will have to wait that time, even if there is no operation performed on all objects. Thus, such systems are mostly used for a single product or when the differences in the products are small.
In other systems, the operations on the objects are performed asynchronous, i.e. the pallet stops at a work station where an operation is to be performed, and is released when the operation is ready. In such systems, a relatively large buffer is required between each work station in order to compensate for the different through-flow times of the products and for the different operation times at a work station.
Another way of compensating for different operation times at a work station is to use two or more work stations that perform the same task. They are often positioned close to each other on separate conveyors, and the object is directed to the work station that is free. In this way, the through-flow time of the system can be balanced in order to avoid bottlenecks in the system. In such a system, the pallets travelling on a single conveyor can be directed to either of the two conveyors by the use of a stop device and a simple switch. Alternatively, a diverter disc may be used to direct the pallets to either of the two conveyors.
Some conveyor systems comprise two infeed conveyors, where a pallet traveling on either infeed conveyor could be directed to any of the two outfeed conveyors. In order to provide such a solution, two stop members and a switch are required. In such a system, a diverted disc cannot be used.
A system using stop members and switches may work acceptable in some cases. Such a solution will require several components and will be relatively slow such that the throughput of the system will be limited. There is thus room for improvements.